RTHistorgramSet does not implement xScale/yScale

RTHistorgramSet does not implement xScale/yScale

The 'histogram' method on SequenceableCollection added by Roassal2 fails due to xScale/yScale not being implemented on RTHistogramSet.

I added implementations of both as:

^ RTLinearTransformation instance.

to RTHistogramSet which at least gets a histogram working. I'm not sure what the proper fix actually is. I thought maybe adding this implementation on RTAbstractDataset would be the right thing to do...